Comparative Efficacy of Biostimulation and Bioaugmentation in Hydrocarbon-Contaminated Soils: A Meta-Analysis with Niger Delta Case Studies

Abstract

Petroleum hydrocarbon contamination poses a major environmental challenge, particularly in oil-producing regions such as the Niger Delta. Bioremediation strategies, including biostimulation and bioaugmentation, are widely applied, but their comparative effectiveness remains uncertain. A systematic review and meta-analysis were conducted in accordance with PRISMA guidelines to evaluate the efficacy of bioremediation strategies in hydrocarbon-contaminated soils, incorporating both Niger Delta and non–Niger Delta studies. Relevant studies were identified through database searches and screened using predefined inclusion criteria, requiring control treatments and quantitative degradation outcomes. Data on total petroleum hydrocarbon (TPH) reduction and treatment characteristics were extracted. Effect sizes were calculated using log response ratios (LRR), and a random-effects model was applied. Subgroup analyses examined differences by strategy and geographic region. A total of 20 studies met the inclusion criteria, with 11 providing sufficient data for quantitative synthesis. The meta-analysis revealed a significant overall effect of bioremediation on hydrocarbon removal (LRR = 2.07; 95% CI: 1.12–3.02), corresponding to an approximately eightfold improvement over natural attenuation. Subgroup analysis showed that combined strategies achieved the highest degradation efficiency (84.8%), followed by biostimulation (77.6%), while bioaugmentation demonstrated lower performance (57.0%); mycoremediation exhibited the highest efficiency (98.4%) based on a single study. Regional comparison indicated comparable performance between Niger Delta (78.9%) and non–Niger Delta (76.2%) studies, although greater variability was observed in the Niger Delta. Sensitivity analysis confirmed the robustness of the findings, with high-quality studies showing a mean degradation efficiency of 81.5%. Although heterogeneity among studies was high, the overall effect remained consistently positive. Bioremediation is highly effective for hydrocarbon-contaminated soils, with combined strategies offering superior performance. These findings support integrated remediation approaches in the Niger Delta, while emphasizing the need for standardized reporting in future studies.